Chemistry 12: Dynamic Equilibrium Practice Test

Transcription

1 Chemistry 12: Dynamic Equilibrium Practice Test A. Multiple Choice: For each question, select the best answer and record your choice on the answer key provided. /25 1) A system at equilibrium is said to be dynamic because at equilibrium the... a) temperature does not change b) macroscopic properties are constant c) forward and reverse reactions continue to occur d) concentrations of reactants and products are constant 2) Which of the following does not apply to all chemical equilibrium systems? a) they are closed b) the macroscopic properties are constant c) forward and reverse reaction rates are equal d) there are equal concentrations of reactants and products 3) Consider the following reaction: N 2 O 4 (g) 2 NO 2 (g) colourless brown If N 2 O 4 is placed in a flask at constant temperature, which of the following is true as the system approaches equilibrium? a) the colour gets darker as [NO 2 ] increases c) the colour gets darker as [N 2 O 4 ] increases b) the colour gets lighter as [NO 2 ] decreases d) the colour gets lighter as [N 2 O 4 ] decreases 4) Consider the following: 2 HBr(g) H 2 (g) + Br 2 (g) Initially, HBr is added to an empty flask. How do the rate of the forward reaction and the [HBr] change as the system proceeds to equilibrium? Forward Rate [HBr] a) decreases decreases b) decreases increases c) increases increases d) increases decreases 5) In which of the following systems will the factors of entropy and enthalpy both favour the reactants? a) PCl 5 (g) + heat PCl 3 (g) + Cl 2 (g) c) NH 4 Cl(s) + heat NH + 4 (aq) + Cl - (aq) b) 3 C(s) + 3 H 2 (g) + heat C 3 H 6 (g) d) Cl 2 (g) HI(g) I 2 (g) HCl(g) + heat 6) Consider the following reaction: Which of the following applies to the forward reaction? C 3 H 8 (g) + 5 O 2 (g) 3 CO 2 (g) + 4 H 2 O(g) ; H = kj Entropy Enthalpy a) increases increases b) increases decreases c) decreases increases d) decreases decreases

2 7) Consider the following equilibrium system: Determine the changes in reaction rates as a catalyst is added N 2 (g) + 3 H 2 (g) 2 NH 3 (g) Forward Rate Reverse Rate a) increases increases b) decreases decreases c) decreases increases d) increases decreases 8) Which of the following graphs shows the reverse rate of a reaction when a catalyst is added to the equilibrium at time = t 1? 9) Consider the following equilibrium: 2 NO(g) + Br 2 (g) 2 NOBr(g) + energy The equilibrium will shift to the products as a result of... a) adding a catalyst b) adding some NOBr(g) c) increasing the volume d) decreasing the temperature 10) Consider the following equilibrium system: CaCO 3 (s) CaO(s) + CO 2 (g) Which one of the following changes would cause the equilibrium to shift left? a) add more CaO c) decrease volume b) remove CaCO 3 d) increase the surface area of CaO

3 11) Consider the following system at equilibrium: H 2 O(g) + CO(g) CO 2 (g) + H 2 (g) This equilibrium will shift right as a result of the addition of some extra H 2 O. How will this affect the concentration of the other gases? 12) Consider the following equilibrium: [CO] [CO 2 ] [H 2 ] a) increases decreases decreases b) increases increases decreases c) decreases increases increases d) decreases decreases increases CaCO 3 (s) CaO(s) + CO 2 (g) H = +175 kj Which of the following diagrams best represents the change in the concentration of CO 2 as temperature is decreased at time t 1? 13) The relationship between K eq and the pressure of a gaseous equilibrium at constant temperature can be described by...

4 14) Consider the following equilibrium reaction: N 2 O 4 (g) 2 NO 2 (g) At time t 1, heat is applied to the system. Which one of the following best describes the equilibrium reaction and the change in K eq? a) exothermic and K eq increases c) endothermic and K eq increases b) exothermic and K eq decreases d) endothermic and K eq decreases 15 Consider the following equilibrium: energy + SbCl 5 (g) SbCl 3 (g) + Cl 2 (g) The K eq decreases when... a) SbCl 5 is added b) SbCl 5 is removed c) the temperature is increased d) the temperature is decreased 16) Consider the following equilibrium: H 2 (g) + I 2 (g) 2 HI(g) Which of the following graphs represents the forward rate of reaction when H 2 (g) is added to the above equilibrium at time = t 1?

5 17) Limestone is decomposed to make quicklime (CaO) according to the following equilibrium: CaCO 3 (s) kj CaO(s) + CO 2 (g) Which of the following would produce the greatest yield of CaO(s)? Temperature Pressure a) low low b) low high c) high low d) high high 18) What will cause the K eq for an exothermic reaction to increase? a) increasing [reactants] b) decreasing [products] c) increasing the temperature d) decreasing the temperature 19) What is the K eq expression for... Sb +3 (aq) + Cl - (aq) + H 2 O(l) SbOCl(s) H + (aq) a) K eq = b) K eq = [H ] [Sb ][Cl ] [H ] [SbOCl] [Sb ][Cl ] c) K eq = d) K eq = [H ] [Sb ][Cl ][H2O] [H ] [SbOCl] [Sb ][Cl ][H2O] 20) Consider the following equilibrium: H 2 (g) + ½ O 2 (g) H 2 O(l) Which of the following represents the concentration of O 2 at equilibrium? 1 2 a) [O 2 ] = K [H ] eq 2 b) [O 2 ] = K eq [H 2 ] 21) Consider the following equilibrium system: c) [O 2 ] = d) [O 2 ] = [H O] 2 K [H ] eq 2 1 K [H ] eq 2 2 CO(g) + Cl 2 (g) COCl 2 (g) At equilibrium, a 2.0 litre sample was found to contain 1.00 mol CO, mol Cl 2, and mol COCl 2. The K eq value for the above system is... a) 2.5 b) 0.20 c) 0.40 d) ) Consider the following equilibrium: Cr 2 O 7 2- (aq) OH - (aq) 2 CrO 4 2- (aq) + H 2 O(l) ; K eq = 4.14 The concentration of ions at equilibrium was measured at a specific temperature and found to be [Cr 2 O 2-7 ] = M and [OH - ] = M. What is the equilibrium [CrO 2-4 ]? a) 1.7 x 10-4 M c) 1.3 x 10-2 M b) 3.1 x 10-3 M d) 2.0 x 10-1 M

6 23) Consider the following equilibrium: 2 NO(g) H 2 (g) N 2 (g) H 2 O(g) Initially, mol NO, mol H 2, and mol H 2 O are placed in a 1.0 L container. At equilibrium, the [H 2 O] = M. What is the value of K eq? a) 3.5 b) 6.5 x 10 2 c) 1.5 x 10-3 d) 1.3 x ) Identify the equilibrium system that least favours the formation of products. a) 2 HgO(s) 2 Hg(l) + O 2 (g) K eq = 1.2 x b) CH 3 COOH(aq) + H 2 O(l) H 3 O + (aq) + CH 3 COO - (aq) K eq = 1.8 x 10-5 c) 2 NO(g) + O 2 (g) 2 NO 2 (g) K eq = 6.5 x 10 5 d) H 2 (g) + Cl 2 (g) 2 HCl(g) K eq = 1.8 x ) Consider the following equilibrium: 2 NOCl(g) 2 NO(g) + Cl 2 (g) A flask is filled with NOCl, NO, and Cl 2. Initially there was a total of 5.0 moles of gases present. When equilibrium is reached, there is a total of 6.0 moles of gases present. Which of the following explains this observation? a) the reaction shifted left because the Trial K eq > K eq b) the reaction shifted left because the Trial K eq < K eq c) the reaction shifted right because the Trial K eq > K eq d) the reaction shifted right because the Trial K eq < K eq B. Written Response: Answer the following questions in detail. For questions involving calculations, answers must include units where appropriate and be given to the correct number of significant figures. Full marks will not be given for providing only an answer. /15 1) Consider the following equilibrium equation: (3 marks) 2 NF 2 (g) N 2 F 4 (g) i) Which way does the equilibrium shift when the volume of the container is decreased? ii) Describe the changes in reaction rates that cause this shift. iii) Does K eq increase or decrease? 2) Consider the following equilibrium: 3 I 2 (g) + 3 F 2 (g) 2 IF 2 (g) + I 4 F 2 (g) Initially, 2.00 x 10-1 mol of I 2 and 3.00 x 10-1 mol of F 2 are put into a L flask. At equilibrium, [I 4 F 2 ] is 2.00 x 10-3 M. Calculate the K eq. (4 marks) 3) Consider the following equilibrium system: 2 COF 2 (g) CO 2 (g) + CF 4 (g) ; K eq = 2.00 A 2.00 L container is filled with mol of COF 2. Calculate the [COF 2 ] at equilibrium. (5 marks)

7 4) Consider the following equilibrium system: C(s) H 2 (g) CH 4 (g) ; K eq = 8.1 x 10 8 at 25 o C A student places 4.5 mol of carbon, 3.6 x 10-3 mol of hydrogen, and 5.1 mol of methane in a 1.0 L flask. The student predicts that the [CH 4 ] increases as equilibrium is established. Do you agree? Explain your answer using appropriate calculations. (3 marks)